1. Field of Invention
Embodiments of the present invention relate to semiconductor devices, and more particularly, to an electrical fuse included in a semiconductor device and a method of manufacturing the electrical fuse.
2. Description of the Related Art
As semiconductor devices are becoming more highly integrated and the storage capacity thereof is increasing, defects are more likely to be formed in memory cells of the semiconductor devices during the manufacturing process of the semiconductor devices, and thereby, causing a decrease in the yield of the semiconductor devices. One of the well-known methods of solving this decrease in yield of semiconductor devices due to the high integration of semiconductor devices is by using a redundant circuit. If a defective main cell is detected by a predetermined test, a fuse in a fuse box corresponding to the defect is selected and opened so that a redundant cell, which is provided around the main cell, replaces the main cell that includes the defect.
The fuse is usually opened by radiating a laser beam that cuts the fuse due to the simplicity and reliability. However, the laser beam cutting method cannot be used in a package level, and as such, it is difficult to reduce the pitch of the fuse. Thus, the laser beam cutting method cannot be applied to semiconductor chips whose size is continuously reduced.
Thus an electrical fuse method, in which a current is supplied in order to cut the fuse, is well known to one skilled in the art and can be applied to solve this problem. In the electrical fuse method, the size of a fuse unit can follow the scaling of a semiconductor device and thereby reduce the occupied surface area in the semiconductor chips while the defective memory cells can be repaired, even in their packaged state.
FIG. 1 is a schematic view of an electrical fuse block for explaining the operation of a conventional electric fuse.
Referring to FIG. 1, the electrical fuse block includes a transistor 1 and the conventional electrical fuse 3 for fuse programming. A pulse voltage Vg is applied to a gate electrode of the transistor 1 to turn on the transistor 1. Then, an over current flows through the transistor 1 into the conventional electrical fuse 3. As a result, the conventional electrical fuse 3 is blown due to the over current that flows through the transistor 1.
FIG. 2 is a top view of the conventional electrical fuse shown in FIG. 1.
The conventional electrical fuse 3 is formed of a cathode 4, a fuse link 5, an anode 6 and contacts 7. The cathode 4 is connected to a drain of a transistor (not shown). When the transistor is turned on, a large amount of electrons migrate from the cathode 4 to the anode 6 through the fuse link 5. As a result, the fuse link 5 is blown. The resistance of the fuse is increased by the blowing of the fuse link 5. As a result, the conventional electrical fuse 3 is substantially opened.
The conventional electrical fuse 3 may be formed of a stack of a metal silicide layer on a polysilicon layer. The blowing of the conventional electrical fuse 3 may be accomplished in one of two modes: a thermo-migration (TM) mode or an electro-migration (EM) mode. In the TM mode, excessive heat is generated by the interaction between electrons and polysilicon elements in the fuse link 5. The excessive heat causes a rupture of the fuse link 5.
FIG. 3 shows a simulation of heat generated during blowing of the fuse link in the conventional electrical fuse shown in FIG. 2.
Referring to FIG. 3, the temperature of a center portion of the fuse link 5 is ten times or more than the temperature of the cathode 4 or the anode 6, and is increased up to several thousands of degrees during the blowing of the fuse link 5. Thus, if too much heat is generated in the fuse link 5, the conventional electrical fuse 3 is blown by a rupture. If the conventional electrical fuse 3 is blown by the rupture, a sensing margin, which is generated by the resistances of the conventional electrical fuse 3 before and after the blowing of the fuse link 5, is not sufficient. As a result, devices adjacent to the conventional electrical fuse 3 may be affected during the blowing of the fuse link 5.